Receiver system



Dec. '6, 1949 FIG. l

Filed March 29, 1944 G. w. BRYAN, JR 2,490,025

RECEIVER SYSTEM 2 Sheets-Sheet 1 INVENTOR.

GEORGE w. BRYAM'JR.

BY M/JMQ/e ATTORNEK De@ 6, 1949 G. w. BRYAN, JR

RECEIVER SYSTEM 2 Sheets-Sheet 2 Filed March 29, 1944 Fics.4 4

FIG.3

I I l l I I l l l l 2 N D DETECTOR 2ND l F CHANNEL 92 LOCAL 9| oscDETECTOR PULSE AMP EWS

CLIPPER FIGS FIG.9

IN VEN TOR. ciones w. BRYAr 1,JR.

A T TORNE )f Patented Dec. 6, 1949 UNI ES PAT E GF FICE RECEIVER SYSTEMGeorge' W.-B`ryan, Jr., Belmar, N. J.

AppuatidniMarchze, 1944; serial No; 528,545

(o1. 250g-2c);

13' Claims.

Inconventionallpulsesecho object detection sys-l" temspulses of:radiofrequencyenergy;in-the-form of discrete Wave trainsfor iixe'd...frequency,J are.v intermittently: transmitted: atiintei-.valsf whichare' relatively large compared toi the:v duration ofl said wave trains;-Oni strikingrlractarget, said pulses are reiiected e and receivedzandr.the 'timeA intervall between the* transmitte'd'l andi.- received;`pulses measuredto determine theldistance of.l saidltarget.- Formeasuring purposeslbothtlie transmittedsignals andthe`rrecel-'Vediechoes:areused..tovertically deflect the beam. ci' anoscilloscope; the' horizontal trace of whichfislformedbymeanslofiasavvf-tooth voltage synchronizedlwith the transmitted-pulses;Instead of defl'ectlng thetbeamg-lthe si'gnalscan be used to varythevlntensit'yofi tliebeaml-'so ytliat they would be indicatedas-avariationin` bright-4` ness of the trace; orbothmethodsf-may' be com` bined. The1 distance between the two:indications on the'oscilloscopetracei`s1a1measure-offthe distance of the yrefle'ctine: object;v

In order tir-provide for accurate measurein'ent';v particularly at shortdistances'sai'd Wave' trains'` must be of extremely'fshort dur-ationToobt'ain` accurate Y definition of1 thelfsharp pulses generated in-such systems. it isnecessary to--usel receivers having wide-bandchan-nels; since? the vvidthof` the side-bands generated? is an inverse'function of the pulse duration. This l-featu're-fcausesconsiderableinterference when a plurality of other units, operating ori-:nearbylfrequencieslwhichf are Within the passLba'nd of:-r said?-cliannelsg arelo"- catedin the saine:area... Sincesuch-:otherl unitsl are usuallynotl'pulsed synchrionously;.4 thisf givesf rise to a. plurality'off'pulse images,.commonly known as railings,. Whichlcontinuonsly; move.one theoscilloscope screen,"4 causing.- considerable*-diffr-A culty inkeeping trackof the; desired.' echoesffand resulting: in; quickLfatiguefofs the@ operatingA per# sonnel. Wide-band channelsalsofacilitate deliberate jamminghrouglt the-usea-of frequency' modulated:or.' amplitude? modulatedsignals which are Within their acceptancelcandl of I said i channels. '.turtl'iermore,` the bandpass.Inecessary.: forl maxi-- 4m resultant'potential'suareapplied tof-the'gridof a=` tube; said' grid being'i sof-'biased thats potentials above apredetermined amplitudef will :drive saidmum denition of` sharp. pulsesis often-v considerably wider than. the band-:pass required for optimum.signalto-noise ratio; sothat the echo signals are further obscured bynoise. currents origihating. both. insideA and. outside the receiver..

Moreover, 'because of the relative weakness of Y the echoes, thereceiver must be made extremely sensitive, rendering it subject to.saturation. or knccldownf by therr strongA transmitted pulses.

In" spite ofv the protective spark-gap networks.

Such-large 'amplitudes Vcause large bias potentials.`

to.. be developed. upon .the receiver tubeelectrodes, which!` potentialscannot. be-dissipated rapidly enoughl by the -R-C-networksassociatedwith said receiver tubes: As: a1 result,.the.receiver. circuits.-

arerendered incapablelof transmittinganyfechoes whichY closelyfollow=the tyDeS of high amplitude signals:abovementionedl It is am'ainobject of thisfinvention toprovide alcircuit whichvv-illeflectively transmit-potentials beloWv a.predetermined.-arnplituda v'and reduce or completely-reject potentialsabove said predetermined4 amplitude. Another object tovprovidef acircuit` which.- will effectively transmit potentials xvithinelapredetermined amplitude-range?andA at-r tenuate or reject` potentialsoutside4 said range;

Still another. object. is tofapplyl-.such circuitstofpulse:modulationlreceivers inforder to1 reduce theablyonthefcrestssthereofga smallhighdrequencya component havingran amplitudewhich'is asmallA fractionof. the amplitudes'of said potentials. The

tube beyond. one of the-bends of its grid voltage-` platecurrentlcharacteristic; er gf, towplatc-cur-L f. rent cutoff.;- before:thecresti of each potentialK is reached -Asa result; thehigh-frequency'com-A ponent on the crests of saidf'potential's'des not appear* inf the1 tubeoutput; Sincefpotentials becomponent" on. the `v crest of saidlower amplitudel potentials 4is transmitted'by saidtube: f Thehighfrequency output of the-:flatter: is new; emphasized r` by anamplifier tuned-to` the" frequency. of said' 55* output andthendetectedtofderiveenvelopesgof the high-frequency component of saidlower amplitude potentials. The latter can now be passed through aconventional clipper circuit which will reject potentials and/or noisecurrents below a predetermined amplitude.

In a pulse-echo receiver, the pulses are already modulated by ahigh-frequency carrier. It is therefore only necessary to pass saidmodulated pulses through a partially-filtered detector which yields aresultant pulse envelope with a portion of the carrier superimposedthereon. The resultant pulses are then handled in the manner abovedescribed.

For a better understanding of the invention, together with other andfurther objects thereof, reference is had to the following descriptiontaken in connection with the accompanying drawings, wherein like partsare indicated by like symbols, and its scope will be pointed out in theaccompanying claims.

In the accompanying drawings:

Figure l is a block diagram of my invention;

Figure 2 is a schematic circuit of a modication of my invention;

Figure 3 is a schematic circuit diagram of my invention as applied to aradio pulse receiver; and

Figures 4 through 9 are theoretical diagrams illustrating the operationof the circuit in Figure 3.

Referring to Figure 1, there is shown a system for discriminatingbetweenpulses of different amplitudes, such as A and B. Such pulses areimpressed on a modulator 2) upon which is also impressed a relativelyhigh frequency (H. F.) potential Z, having a period which is relativelysmall compared to the duration of each pulse. Modulator 2l) is normallybiased at or below cutoff so that normally there is no H. F. componentin its output.' Pulses A and B will render the modulator increasinglyconducting, so that its output will contain pulse modulated H. F. pulsesor wave trains AZ and BZ, corresponding in amplitude to pulses A and B,respectively.

The H. F. output of modulator 20 is now, if desired, amplified by anamplifier 2|, tuned to the frequency of said H. F. potential Z, andimpressed upon a partially-filtered detector 22, hereinafter describedin greater detail. This detector will yield negative-going pulses Al andBI, corresponding in amplitude to wave trains AZ and BZ, respectively.Because the detector 22 is partially ltered, a small H. F. component ZIwill ride on the crest portion of pulses Al and BI.

The output of detector 22 is now impressed upon the grid circuit of anamplitude discriminator 3, which is essentially a vacuum tube with itsgrid so biased that negative-going pulses, such as Al, which are above apredetermined amplitude represented by dotted line Q, will drive saidgrid to plate-current cutoff, while pulses such as Bl, which are belowsaid amplitude, will not drive said grid to cuto. As a result, H. F.component ZI on pulse Al will not appear in the output of said tube,while said H. F. component of pulse Bl will get through.

The output of amplitude discriminator 23 will therefore contain a pulseA2 without any H. F. component thereon, and a pulse B2 with H. F.component Z2 on the crest thereof. Component Z2 may, if desired, befurther amplied by H. F. amplifier 2e tuned to the frequency thereof orto a harmonic of said frequency. This amplifier rejects pulse componentsA2 and B2, and yields 4 a wave train BZ3, representing the amplifiedcomponent Z2. Wave train BZ3 is then detected by a conventional detector25 which yields the envelope BZt of wave train BZ3. Thus, from anoriginal pair of input pulses A and B of different amplitudes, only asingle pulse BZll, derived from smaller amplitude pulse B, appears inthe output.

Figure 2 illustrates a simplied version of the system above described.This version includes a mixer 25A, comprising a pentode 35, which may beof the 6SJ7 type, and which has its cathode normally biased positivewith respect to its grid 32, by means of a potential drop across aportion of potentiometer 34 connected in series with iixed resistors 36and 38 across the terminals l5 and l2 of a plate voltage source. A smallH. F. potential Y is impressed across a choke 44 in the cathode circuit,which choke may be tuned to the frequency of potential Y. A bypasscondenser llt provides a low impedance path to ground for H. F.potential Y. By adjusting the slider of potentiometer 3d, the negativebias is made high enough to bias the grid sufficiently belowplate-current cutoff so that H. F. potential Y does not normally appearacross the output resistor 6.8 of tube 35.

Positive-going pulses C and D, having different amplitudes, areimpressed across a potentiometer 55. A selected portion of the pulseinput, as determined by the setting of slider 52, is impressed on thegrid 32. Slider 52 is so adjusted that the positive-going pulses renderthe grid suiciently positive to overcome the cutoff bias and render thetube conducting. If the amplitudes of pulses C and D are made largecompared to the amplitude of H. F. potential Y, the resultant potentialsacross output resistor 48 will be in the form of negative-going pulsesC! and DI (due to phase inversion by the tube) with a small H. F.modulation component YI riding on the crests thereof.

Resultant pulses Cl and DI are impressed, through condenser '55 of lowimpedance to all pulse components, upon the input resistor 56 of anamplitude discriminating circuit 23A, corresponding to component 23 inFigure l. Circuit 23A includes a pentode tube 58, preferably of thesharp cutoff type such as type 6AC7, having its grid @il normally biasedat zero or slightly negative potential so that it is normallyconducting. A negative-going pulse such as Cl which is above apredetermined amplitude such as represented by line R, will drive grid6B suiciently negative to bias tube 58 to plate current cutoff. As aresult, the H, F. component YI will not appear across output resistor 62of tube 58, as shown by pulse C2, while pulse DI, which has an amplitudeless than R, will appear across resistor 36 as a pulse D2 together withits H. F. component Y2. Component Y2 can now be amplied and detected byelements such as 24 and 25 in Figure l.

The suppressor grids of tubes 35 and 58 are connected to ground, asshown. The screen grids are connected to the plate-supply source througha voltage dropping resistor 38.

Reference is now made to Figure 3, which shows the above-describedexpedients applied to reduce the effects of interference and otherundesirable potentials in a pulse-modulated carrier receiver, such asthat of a pulse-echo object detection system. Said receiver is usuallyof superheterodyne type and comprises a conventional carrier channel2lB, including a directive antenna array l5, the carrier output of whichis mixed with the output of a local oscillator 12 in a rst detector 14-tojderive an immediatefrequency (I. F.-) carrier, whichl is amplified bya first4 intermediate freq uency amplifier channel I 6.

In a conventional receiverl systenuthe signalsV in the output ofy Ir.Echannel-fflare'detected to derive the signal envelopes which, in thecase of a pulse-echo system, are in theilorm-ofipulses. Said pulses arethen amplified in a videopulse amplier 27, and/then usedto control-thebeam ofjan oscilloscope 281170 Provide/indications.which maybeinterpreted, by meanswellknownin the art, to locate a reilec'ting object.`

I-lowever, for reasons above mentioned., interfering signal-s and lnoisewiIl'a-ppear on-theoscilloscope screen togetherwith 'the echo-sig'nalsfand -will make interpretation off-the echoes@ difficult.- Thiswillbe evidentfroman examinationofFigure 4 which is a simplifiedrepresentation, 'on an exaggerated scale, of signals Which-maybefpresent in the output 4of I; FL amplierf'lfduri-ng one cycle of theoscilloscope sweep.- Pulsemodulated wave trains l2v .and`E-representthe-'main trans.- mitted pulses and the echo pulses,respectively. Wave trains F, G; andH represen-t interfering signalsofthe -raili ngstype, which are rarely, if ever, synchronizedwith thetransmitted -pulses and therefore move back and forth'relative 4to theother signals so that they intermittently `coincide with, and thusobscure, thedesiredecho signals E. Signals P, F, G; and Hare almostalways of much greater .amplitude than theeechoes E, and causesaturation (or knockdown-)- of-the receiver a-s above explained. Inaddition, there appear signals such as K; 4which may be considered asrepresenting noise currents, originati-ngboth inside and outside thereceiver,andinterference due to continuous waves, which may oe-either unmodulated or modulated in amplitude or-frequency.

`All the above interfering currents can be reduced or eliminated byapplying to the receiver system the expedients above'd'escribed Viinconnection with Figures land 2'.y Thus ,rthe output of I. F. amplier 16is applied,v through'a condenser 80 of low impedance to theI-.fF,'-currents, toa partially-iiltered second detector 22B; comprisinga pentode 8|, preferably of the 6SJ75'=type, having a tuned grid circuit82 and an output resistor 83.

'Iheinput gri'df84is biasedrabboutirvoltsnegatively with respect-tothecathode, so that:itoperates ori-the lower .bendofitsgrid voltage-platecurrent characteristic. Platek and. screen.. potentials. :are derivedfroma potentiometer 'netwerlrllE. The suppressor gridlisgroundedasshown.

This detector -is-Aconventional'except-inthe following respect:Ord-i-narilytherenis'nsed-anrI. F.l bypass condenser 86,IwhichL-isilargeenough'to bypasssubstantially all theI.E.fcarriercomponents, so that onlyl the pulsemodulatiomenvelopeappears across load resistor 83. Inthe presentcase, however, condenser64 isof higher-impedance so that .a portion of the I. Ffcarriercomponent'appears across load resistor `83,superimposed-on the pulseenvelope.

T-hefterrn partially-,ltered.detector :as applied to the detector -22Bwill now `be` clearfrom` the above description. As used in thespeciiication and claims the ter-m partially-filtereddetector is denedas a detector in` which thecarrier component is notcompletelyfby-passed, so that a portion of the carrier componentremainssuperimposedl on thelpulse or modulationenvelopef The outputacross loadfresistor lIl?, isillustrated irl-Figure 5.- Inthis Vfigure..as wellaas y Figures 6-9, all signals whichl are developed inthe suc.

ceeding circuits from original-signals P,- E, F; G,

diierentiated Joy different numericalsubscrlpts.

Thus, pulses Pl and El, inA Figurel, are derived from signals P and Ein-Figuretetc. As. is shown in Figure 5, the rectiiyingacti0n-of1detec--tor 22B results in negative-going -pulseenvelopes with a small I. F.carrier component WI riding on the crest of each pulse envelope. Saldi..EJ component should .preferablyhave an amplitude ywhich is about 10% ofthepulse amplitude.

The pulses acrossresistor 83-arenowimpressed, through a low impedance:blocking condenser 81; uponthe input grid ofa pentode-tube siofariamplitude fdiscriminator 23B, whiohis substan tially similar instructure and operationtocomponent 23A in Figure 2. As aresult,pulses-such as Pl, Ft, Gi, and HI,- which havean-.amplitudel higher thana predetermined amplitude, suchas. indicatedby dotted line Q, willdrive-thev ygrid of tube 68 to plate-current cutoff before sai-d pulsesreach their maximum amplitude, sothat the I; F. component ori-thegrid-of-said pulses will not appear across the outputresistorvittici-tubev 88.

The resultant potentials across output resistor ilg'are shown in Figure6. It-'will-be--seenthat .pulses P2, F2, G2, and H2 have no I. F. components superimposed thereon, While echo pulse-E2 still has an I. F.component-vWzfthereon, sincedlt is derived from signal El -whichhasaloweramplitude level than that indicated-by line Q."

By Iproviding means to vary-the Soia-s onlthefinput grid of tube `Sii,the lplate-currentl cutoff level., represented -by line Q, canloe-adjusted sothat any desired signal level cany reaehinto the cutoffregion. A preferable method, howeven'is. to leave the hias fixed, anddetermine theI signallevels which reach into the cutoirregion-by.merely-ade j-usting the gain control associatedfwith thexfl-rst carrierchannel 2 IB. Thevoltages across resistor 89 are now impressed, throughablockingcon denser of low impedance tothe I. F.- component W2, upon asecond vI. F. ampli-erchannel 24B, Awhich ampliiies -said I. F.componentbutdoes not transmit the pulse components. 'Ihe-signals-intheoutput of amplifier 24B' are/shown in Figure '7.v Since there is noI. F. componentfon pulses P2, F2, G2, and H2, no output representinglthese signals appears in the -output circuit of-amplifier 24B. But theI. F. component-l W2=ofvpulse EZf'is amplied and appears as a pulsemodulated I. E. signal EWS. Noise and amplitude modulated carriersignals K3 still appear in the output, however; if the amplitudesthereof arebelow-thelevel .indicated by line Q. (Figure 5.)

The output of the second I. Fr amplier 24B is now detected in athird-detector 25B, of vconventional design, which yieldsthe-pulseenvelopes EW- of all the I. F. signals, as-indicatedin'Figure 8. If itis desired toelimin-ate all the lower amplitudenoise and interferencecomponents K4., the output of detector 25B can bepassed through aconventional clipper circuit 26 which will pass only signals above a,predetermined amplitude level, such as indicated by line L, in Figure 8SThe output of 'clipper 2S can nowbe inverted land/or aampliiied in avideo pulse am'plifier'Z'l to yield a signal such as EWS in Figure9,-andthen--im- `pressed on oscilloscope 28.

It ywill be obvious thatthe system in' Figure-3 is similar to thatinFigure `1. In--the latterthe pulses are first mixedwith ahighlv-irequencyfcomponent-in a modulator 20s-y The-resultant modulatedpulses yare thenV appliedto an amplifier 2| tuned to said high frequencycomponent. In Figure 3, the mixing process is not necessary since thatis done in the pulse transmitter (not shown) of the pulse-echo system.The waves received by the antenna are therefore handled in a carrierchannel 2IB, which is the equivalent of channel 2I in Figure l.Similarly, I. F. ch-annel 24B in Figure 3 is the equivalent of channel24 in Figure 1.

Although the operation of the above circuits has been illustrated inconnection with discrete square pulses, it should be understood that thesame techniques can be used with other wave shapes. In general, the moresharply rising the pulses handled, the better the circuits perform.

The system in Figure 3 is capable of several modes of operationdepending upon the variety and extent of interference present. As abovepointed out, the carrier channel ZIB should have a band-pass wide enoughto pass the entire sideband of the pulse modulated carrier in order toget faithful resolution of the desired ech-o-pulse signals. The narrowerthe pulses, the wider the side-band produced. The band-.pass of bothcarrier channels ZIB and 24B should, therefore, be at -least as wide asis necessary to accommodate the side-band spectrum of the desired .pulseechoes.

However, a band-pass wide enough ito provide good resolution of thedesired pulses is usually wider than that required for maximumsignalto-noise ratio. If noise is excessive, it can be reduced bynarrowing the bandpass of the carrier channel, but if this is done inthe first I. F. channel ZIB, as would be the case in a conventionalreceiver, it would result in a distortion or widening of the pulses inthe channel output, causing 'diiliculty in distinguishing closely spacedechoes from each other and aggravating the efects of interfering pulses.It also reduces the accuracy with which the distance of `anecho-producing body can be determined.

These diculties can be considerably reduced in the system shown inFigure 3, by making the band-pass of channel 24B narrower than that ofchannel 2 IB. Thus the band-pass of channel ZIB can be made wide enoughto .provide for maximum resolution of the desired pulse echoes, whilethe band-pass of channel '2aB will be just wi-de enough for optimumsignal-to-noise ratio, or said band-pass can be made even narrower thanthat necessary to obtain maximum signal-to-noise ratio if it is desiredto eliminate strong adjacent channel interference of the continuous wavetype. This may distort the desired pulses somewhat, but the result willnot be so serious since all large amplitude interference components,such as railingsj are not presen-t in channel 24B `and therefore cannotobscure the desired echoes.

To facilitate the design of a narrow band channel, the frequency of theI. F. output of network 23B can be changed, by means of an additionalheterodyne `converter or second detector 9| and local oscillator Q2, toa lower frequency to which the second I. F. amplifier of channel 93 canbe tuned. The second detector 9|, local oscillator 92, and second I. F.amplier 93 constitute a second I. F. channel 24B.

Another mode of operation is necessary when it is desired to eliminatethe effects of interfering pulses, or railings which are of much shorterduration and greater amplitude than the desired echo pulses, and theinterval between the interfering .pulses is very small, eg., thespaceto-markratio is unity or less. If the band-width of the carrierchannel ZIB is just adequate to provide good resolution of the desiredecho pulses, said band-width will be insufcient to adequately resolvethe narrower interfering pulses. As a result, the latter pulses will bewidened so that they ltend to cover up the spaces therebetween `andcompletely cover the desired pulses.

To reduce this effect, the rst carrier channel 2 IB should have a wideenough band-pass to adequately resolve the narrowest interfering pulsesto be handled. This will result in a noise bandwidth `which will be muchlarger than in a channel which would be just wide enough to resolve ithedesired wider pulses. However, by making the band-pass of channel 24Bjust wide enough to adequately resolve the wider echo pulses, theadditional noise currents passed by channel ZIB can be eliminated. Sincethe interfering pulses -will be .blanked out by circuit 23B due to theirlarger amplitude, the desired wider pulses in the output of channel 211Bcan be observed between the spaces represented by the blanked-outinterfering pulses.

To permit selection of the various modes of 0D- eration above described,channels 2IB and 24B should have variable selectivity control means topermit adjustment of the effective band-widths of said channels.

Although blanking of high amplitude signals has been accomplished byderivingr a negativegoing pulse envelope from partially-filtereddetector 22B, and then vusing said envelope to ldrive the grid of tubein amplitude discriminator 23B to plate-current cut-on", the same resultcan be obtained with positivegoing envelopes by causing the latter todrive said tube beyond the upper bend of its plate currentcharacteristic, i. e., lto saturation.

While there has been described what is at present considered aypreferred embodiment of the invention, itwill be obvious to thoseskilled in the arlt that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims, to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

I claim:

1. The method of discriminating between electrical Ipulses of diierentamplitudes Iwhich comprises superimposing on said pulses an electricalwave component having a period considerably smaller than the duration ofsaid pulses and having an amplitude which is a minor fraction of theamplitude of said pulses, extracting the wave component of only thosepulses which are below a predetermined amplitude, and :amplifying anddetecting said extracted wave component to derive resultant signals inresponse to the smaller pulses.

2. The method of discriminating between incoming modulated carrier wavesof diferent :amplitudes which comprises deriving from said waves theenvelopes thereof and a small component of the incoming carrierfrequency waves superimposed on said envelopes, `extracting from saidyderived envelopes the carrier frequency component of only thoseenvelopes which are below a predetermined amplitude, and detecting saidextracted carrier frequency components to derive resultant signals.

3. The method of discriminating between incoming pulse modulated carrierwaves of different amplitudes. which comprises deriving from saidlwavesthe pulse envelopes thereof and a small componentnof the incomingcarrier frequency Waves superimposed on said envelopes, extracting fromsaidf-derivedjpulse envelopes only the carrier frequency component of`those: envelopes which ,are below apredetermined amplitude, andamplifying and detecting said extracted carrier frequency components toderive resultant signals.

A 4.*Thle kmethod of discriminating between incoming pulse modulatedradio frequency carrier waves of different amplitudes which comprisesdetecting and partially bypassing said Waves to derive the lpulseenvelopes thereof and a small component of the incoming carrierfrequency waves superimposed on the crest of said envelopes, extr-actingfrom said derived pulse envelopes the carrier frequency component ofonly thoseenvelopes which are below a predetermined amplitude,amplifying and detecting -said extracted carrier frequency componentsIto derive resultant` signals, and selectin-g from saidresultantsigr'ialsonly those above a predetermined amplitude.

5. An amplitude discriminating receiver system for incoming modulatedcarrier waves which com- :prises a detector for `deriving from saidwaves the in'f'idulatio'ri envelopes thereof, means for super'-impo'sin'g'on said envelopes a portion of said incoming carrier waveswhich is of substantially smaller amplitude than said envelopes to forma resultant wave, a grid-controlled electron tube having its gridexcited by said resultant wave, the bias on at least the grid of saidtube being such that envelopes above a predetermined amplitude willdrive said tube beyond at least one of the bends yof its gridvoltage-plate current characteristic whereby a smaller portion of thecarrier component on modul-ation envelopes which are above saidpredetermined amplitude will be transmitted by said tube, and meansresponsive to said carrier component coupled to said tube.

6. An amplitude discriminating network for incoming pulse modulatedcarrier waves which comprises means for deriving pulse envelopes of saidwaves with a small component of said incoming f carrier frequency wavessuperimposed on the crest thereof, a sharp cutoff electron tube havinginput and output electrodes and having its input electrode excited bythe voltage output of 'said means, the Ibias on at least one of saidelectrodes u being such that pulse envelopes above a predeterminedamplitude will `drive said tube beyond one of the bends of its inputelectrode voltage with respect to its output electrode currentcharacteristic, whereby the carrier component of said pulse envelopeswhich are above said predetermined amplitude will be more effectivelyattenuated by said tube, filtering -means for selecting the carriercomponent from the output of said tube, and an additional detectorcoupled to the output electrode of said tube.

7. An amplitude discriminating network `for pulse modulated carrierwaves which comprises a detector excited by said waves having means foronly incompletely removing the carrier component of said waves forderiving negative-going :pulse envelopes of said waves and a smallcarrier frequency component superimposed on each envelope, the amplitudeof said carrier component being a minor fraction of the amplitude ofsaid envelope, an electron tube network having its input circuit excitedby the voltage output of said detector, the bias on at least one of theelectrodes of said tube being such that pulses above a predeterminedamplitude will drive said tube to plate-current cutoff befre saidpulsesreachther full amplitude, whereby only the carrier componentassociated with envelopes which are below said predetermined amplitudewill be transmitted by said tube, an amplifier tuned to the frequency ofsaid carrier componenti*l for amplifying the carrier output of saiddetector, an additional detector coupled to the output of said tunedamplifier, and a signal utilization means controlled by the output ofsaid additional detector.

8. An amplitude discriminating receiver system for pulse modulatedcarrier rwaves which comprises a rst tuned amplifier for said carrierwaves, a detector having means for only incompletely removing thecarrier component of, said waves 'for deriving -pulsegenvelopes of saidwaves with a small carrier component on the crest porrtion of each ofsaidpulse envelopes, a grid-controlled electron tubeinetwork having itsgrid circuit excited by the voltage output of said detector, the bias onthe grid of said tube being such that pulse envelopes above apredetermined ampli-tude will cause said tube to operate beyond one ofthe bends of its grid voltage-.platecurrent characteristic before saidenvelopes. reach their maximum amplitudes, whereby only the carriercomponent on the crest of those pulse envelopes ,which 'are below saidpredetermined amplitude will be transmitted by said tube a secondamplifier vtuned to the frequency of said carrier component foramplifying the carrier output of said detector, an additional detectorcoupled to the output of said second amplifier, and signal translating`means controlled by the output of said additional detector. a ,A

9. An amplitude discriminating system for pulse modulated carrier waveswhich comprises a first tuned amplifier excited by said waves and tunedto the frequency thereof, a detector having means for only incompletelyremoving the carrier component of said waves for deriving negative-goingpulse envelopes of said waves with a small carrier component on thecrest portion of each envelope, an electron tube network having itsinput circuit excited by the voltage output of said detector, the biason at least one 0f the electrodes of said tube being such that pulsesabove a predetermined amplitude will drive said tube te .plate-currentcutoff before said pulses reach their maximum amplitude, whereby onlythe carrier component on the crest of said pulse envelopes which arebelow said predetermined amplitude `will be transmitted by said tube, asecond amplifier tuned to the frequency of the carrier component foramplifying the carrier output of said tube, said second amplier having anarrower band-pass than said first amplifier, an additional detectorcoupled to the output of said second amplifier, and signal translatingmeans controlled by the output of said additional detector.

10. A system as set forth in claim 9, including means to reduce thefrequency of the carrier outiput of said detector to a lower frequency,said second amplifier being tuned to said reduced frequency.

11, An amplitude Idiscriminating receiver system for pulse modulatedcarrier waves which comprises an antenna for receiving said waves, a rstdetector coupled to said antenna and to a source of heterodyningoscillation-s for deriving pulse modulated intermediate frequency waves,a first tuned amplifier for said intermediate frequency waves, a second'detector having means for only incompletely removing the intermediatefrev4aandoet quency component for deriving negative-going pulseenvelopes of said waves with a small intermediate frequency componentlon the crest prtion of each envelope, a grid-controlled electron tubenetwork having its grid circuit excited by the voltage output of saidsecond detector, the bias on said grid being such that :pulses above apredetermined amplitude will drive said tube to plate-current cutoffbefore said pulses reach their full amplitude, whereby only theintermediate frequency component on the crest of said pulse envelopeswhich Iare below said `predetermined amplitude will be transmitted bysaid tube, a second amplifier tuned to the intermediate lfrequency foramplifying the intermediate frequency output of said tube, said secondtuned amplifier having aV narrower band-pass than said first tunedamlplier, a third detector coupled to the output of said second tunedamplifier, a clipper circuit coupled to said third detector fortransmitting only voltages above a predetermined amplitude, and signalreproducing means controlled by the output of said clipper.

12. A system as set forth in claim 11, including additional heterodynemeans to reduce the fre- Y quency of the intermediate frequency outputof 12 carrier waves without appreciable distortion of their .pulseenvelopes, means including a detector coupled to said filter 4forderiving the pulse envelopes of said desired and undesired carrierAwaves and for superimposing la small component of the incoming carrierwaves on the crests of said envelopes, means excited by the output ofsaid detector to so limit the amplitude of said output that only thecarriei' component on the crests of envelopes derived from said desiredwaves of said predetermined amplitude are transmitted, a second carrierwave filter coupled to the output of said discriminating means andhaving a band pass which is wide enough to pass the modulation componentof the waves in the output of said apparatus, yand signal translatingmeans coupled to the output of said second filter.

' GEORGE W. BRYAN, JR.

REFERENCES CITED The following references are of record in the ille ofthis patent:

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